We propose to study by ultrastructural cytochemical methods the localization, in particular the cell surface topography, of ectoenzymes, lectin binding sites and sialic acid residues, and the possible modulations of such topography induced during cell locomotion and phagocytosis. Possible mechanisms of control of topography will be investigated, particularly in regard to the possible roles of microtubules and microfilaments, as derived from studying the effects of topography of colchicine, cytochalasin-B and other drugs. Ultrastructural cytochemical methods for the ectoenzyme 5'-nucleotidase on polymorphonuclear leucocytes (PMN) and lymphocytes will be applied. In PMN the modulation of localization of this enzyme during phagocytosis and cell movement will be studied. In lymphocytes the class of lymphocyte bearing the enzyme will be established, in part by combining autoradiography of anti-Ig binding to B cells. Modulation of localization during locomotion and capping will be established. In PMN, a new cytochemical method for NADH-oxidase and NADPH-oxidase, localizing the sites of H2O2 production in resting and phagocytizing cells will be applied in similar vein. Possible similar modulations in lectin binding sites and sialic acid residues on PMN, lymphocytes and virally-transformed cells will also be investigated. In the latter system, correlation of surface modulation with changes in distribution of intramembranous particles will be done. Efforts will be made to develop scanning microscopy as a tool for studying cell surface topography as delineated by ultrastructural cytochemical methods.